Preparation of organopolysiloxanes containing silicon-bonded carboxyalkyl groups



UnitedStates Patent PREPARATION OF ORGANOPOLYSILOXANES CONTAINING SILICON -BONDED CARBOXY- ALKYL GROUPS Ben A. Bluestein, Schenectady, N. Y., assignor to Generai Electric Company, a corporation of New York No Drawing. Application March 20, 1957 Serial No. 647,192

4 Claims. (Cl. 260-465) I. m 4-m (hereinafter referred to as organoalkoxysilane) where Ris a member selected from the class consisting of monovalenthydrocarbon radicals and halogenated monovalent hydrocarbon radicals, R is a lower alkyl radical containing from 1 to 5 carbon atoms (e.g., methyl, ethyl, propyl, butyl, isopropyl, amyl, etc.), and m is a whole number equal to from 1 to 3, inclusive. Examples of what R may represent are given below.

duly large amounts of polymers derived from the individual starting chlorosilanes. One attempt to overcome.

this obstacle has been to attempt to react aqueous solutions of carboxyethylpolysiloxanes with cohydrolyzable organochlorosilanes; however, this technique gave no indication of homogeneous copolymer formation.

Unexpectedly, I have discovered that I am able to make copolymeric organopolysiloxanes containing carboxyalkylsiloxy units and intercondensed organosiloxy units in which the organic group is free of carbon-bonded carboxyl groups, if one employs for co-reaction purposes an aqueous solution of a carboxyalkylpolysiloxane and an organoalkoxysilane of the formula R Si (OR) where m, R and R have the meanings given above; Among the water-soluble carboxyalkylpolysiloxanes which may be employed in the practice of my. invention are those which have the formula 1 Thus, the cyanoalkylpolysiloxane of In the copending application of Glenn D. Cooper and Maurice Prober, Serial No. 529,896, filed August 22, 1955, and assigned to the same assignee as the present invention, there are disclosed and claimed liquid and solid organopolysiloxanes having the average composition (HOOCC H2 RbSiO4 where the HOOC group is attached to a carbon atom other than a silicon-bonded carbon atom, R" is a monovalent hydrocarbon radical, for instance, methyl, ethyl, propyl, cyclohexyl, phenyl, diphenyl, naphthyl, tolyl, benzyl, and halogenated aryl radicals, for example, chlorophenyl, dibromophenyl, etc., radicals; n is an integer equal to from 2 to 18, inclusive, and preferably from 2 to 5 inclusive; a has a value of from 0.01 to 2.0; the sum of a-t-b is from 1.0 to 2.5, inclusive. The R group may be on the same silicon atom. as the carboxyalkyl group or may be on a different silicon atom.

When one attempts to obtain the above-described carboxyalkylpolysiloxanes by (1) the cohydrolysis of chlorosilanes composed of, for instance, cyanoethyltrichlorosilane and other cohydrolyzable organochlorosilanes, for instance, dimethyldichlorosilane, trimethylchlorosilane, methyltrichlorosilane, diphenyldichlorosilane, etc., and (2) hydrolyzing the cyanoalkylpolysiloxane to the carboxyalkylpolysiloxane, one finds that the usual methods for making such copolymers by cohydrolysis are attended by a marked tendency toward homopolymerization. Thus, if one tries to copolymerize trimethylchlorosilane with cyanoethyltrichlorosilane, because of the difference in the rates of hydrolysis, the cyanoethyltrichlorosilane may hydrolyze and polymerize in advance of the trimethyltrichlorosilane. sothat the reaction-hydrolysis product may contain, in addition to copolymeric materials, un-

nooccnn sio where n is an integer equal to from 2 to 4. These compositions, which may be obtained by hydrolyzing cyanoalkylpolysiloxanes of the formula NCC H SiO where nhas the meaning given above, may contain polysiloxane molecules of the above formula having siliconbonded hydroxyl groups of silanol groups which addto the water-solubility. The cyanoalkylpolysiloxanes used for this purpose and methods for preparing the same. are more particularly disclosed and claimed in the copending application of Maurice Prober and Serial No. 401,701 filed December signed to the same. assignee as the Glenn D. Cooper,

present invention. the above formula may be hydrolyzed in an alkaline or acidic aqueous medium to convert the cyanoalkyl radicals attached to silicon to carboxyalkyl radicals.

The cyanoalkyl polysiloxanes can be prepared by the hydrolysis of the various silanes which contain both silicon-bonded chlorine atoms and silicon-bonded cyanoalkyl radicals.

The silanes containing both silicon-bonded chlorine and silicon-bonded cyanoalkyl radicals are prepared by the method disclosed in the copending application of Cooper and Prober, Serial No. 401,704, in the copending application of Maurice Prober, Serial No. 401,702, both applications being filed December 31, 1953, and in U. S. Patent 2,776,306 of Quintin P. Cole issued on January 1, 1957, the applications and patent (which by reference are made part of the disclosures of the instant application) being assigned to the same assignee as the present invention. For example, silanes containing both a cyanoalkyl radical and chlorine atoms attached to silicon may be prepared'by refluxing, for instance, methyldichlorosilane, trichlorosilane, etc., in the presence of a trialkyl amine such as tributyl amine, and a suitable nitrile containing olefinic unsaturation. Suitable nitriles include, for instance, methacrylonitrile, alpha ethylacrylonit rile, crotononitrile, acrylonitrile, etc. These compounds contain three chlorine atoms attached to silicon andmay be converted to a dichlorosilane. For example, methyl betacyanoethyldichlorosilane may be prepared by refluiring betacyanoethyltrichlorosilane with methyl magnesium bromide. The same compound may also be prepared by reacting betacyanoethyltrichlorosilane with dimethyl cad mium.

aforementioned Prober and Cooper application, Serial No. 401,701. Thus, the cyanoalkylorganopolysilorane Patented Feb. 24, 1959;

31, 1953, and as T 2,875,177 V p fluid may be prepared by hydrolyzing a compound, such as cyanoethyltrichlorosilane, by agitating the silane for several hours in water or in as mixture of ether and ice.

lnhydrolyzing the cyanoalkylpolysiloxane to the corresponding carboxyalkylpolysiloxane, the amount of acid or base employed is not critical since the acid or base acts only as a catalyst. However, for convenience, one advantageously employs relatively large amounts of the acid or base. since the hydrolysis of the reaction is speeded up thereby. Thus satisfactory hydrolysis of the cyano' alkylpolysiloxanehas been obtained using from 0.1 to 20 or more equivalents of acid or base. per cyanoalkyl group. Further directions for making the cyanoalkylpolysiloxanes and the hydrolysis of the latter to carboxyalkylpolysilanes may be found in the copending application of Glenn D. Cooper and Maurice Prober, Serial No. 529,896, filed August 22, 1955, which by reference is made part of the disclosures of the instant application.

The carboxyalkylpolysiloxane, which should be soluble in all proportions in water, is advantageously employed in molar concentrations ranging from 0.1 to 95 mol percent while the other copolymerizable organoalkoxy silane of the Formula I is employed in amounts ranging from about 5 to 99.9 mol percent. The carboxyalkylpolysiloxane is advantageously dissolved in water in con centrations ranging, by weight, from to 90 percent solids based on the total weight of the water and the carboxyalkylpolysiloxane.

In preparing the mixture of the aqueous solution of the carboxyalkylpolysiloxane and the organoalkoxysilane, it is only necessary to dissolve each of these two ingredicuts in the desired proportions, employing moderate heat.

if desired. Gently warming the reaction mixture at temperatures ranging from about 30 to 75 C. accelerates the cohydrolysis and intercondensation of the product.

Thereafter the intercondensed reaction mass. can bev isolated by evaporation of the water employing preferably vacuum and lower temperatures in order to avoid undue condensation of the formed organopolysiloxane. Be-

cause of the large amount of trifuncti'onal siloxy units present due to the use of, for instance, carboxyalkylpolysiloxanes of the formula HOOCC HznSiO 2 where n has the value given above, the reaction mixture should be dried carefully at temperatures of from 40 to 7 5 C. to obtaina product which can be readily molded or dissolved in suitable organic solvents as well as. in water to make treatingsolutions for impregnating and coating purposes. Upon heating the intercondensed carboxyalkyl organopolysiloxane (containing silicon-bonded carboxyalkyl groups and silicon-bonded R groups) at elevated' temperatures (e. g., at 125 to 200 (3.), the intercondensation product will further condense and convert to the substantially cured, solid state.

-.In order that those skilled in the art may better understand how the present invention may be practiced, the following examples are given by way of illustration and not by way of limitation. All parts are by weight.

Example 1 the silicon-bonded chlorine, and then refluxing the cyano ethylpolysiloxane with aqueous sodium hydroxide weight percent) to form the. sodium salt of carboxy ethylpolysiloxane of the formula where x is an integer greater than 1. The sodium salt is converted to the carboxyethylpolysiloxane by acidification of the sodium salt, with subsequent isolation of the resulting carboxyethylpolysiloxane precipitate. To three solutions made by combining 35.6 parts (0.28 mol) (CH Si(OC H with 160 parts H O (maintained at a temperature of about 80 C.) were added, respectively, 1 part, 3 parts, and 6 parts (each in 10 parts water) of the above-prepared carboxyethylpolysiloxane. The resulting reaction products were dried at C. for about four hours to give, in each instance... a cross-linked, solid prod. not. The. aforesaid co-reaction product appeared, to be intimately interreacted without any evidence of homopolymerization. The product contained intercondensed dimethylsiloxy units and carboxyethylsiloxy units.

Example 2 of a hard solid which comprised intercondensed carboxyethylsil'oxy units of the formula HOOCC H SiO and dimethylsiloxy units. The solubility in water of these solid materials increased with decreasing concentrations of the starting dimethyldiethoxysilane.

It will, of course, be apparent to those skilled in the art that other water-soluble carboxyalkylpolysiloxanes, many examples of which have. been given before, may be employed in place of the carboxyethylpolysiloxane used in the. foregoing examples without departing from the.

scope of the invention. In addition, it is intended that.

other types of organoalkoxysilanes can be used, as well as varying concentrations of the latter in combination with carboxyalkylpolysiloxanes.

The carboxyalkylpolysiloxanes of the present invention are useful for many of the applications which organopolysiloxanes containing only silicon-bonded alkyl,

aryl, or haloaryl radicals are useful. Thus, the carboxy-.

alkylpolysiloxanes prepared in the above manner are useful as emulsifying agents or as surface active agents. In addition, these compositions can be used as impregnating agents for fabrics and then heated to impart water-repellency to the fabrics. Carboxyalkylpolysiloxanes prepared in accordance with the above described process can also be employed in cutting and sandin ap plications because they are, able to be, converted by heat to hard, abrasion-resistant products. which have good resistance to heating at elevated temperatures. They are also useful as intermediates in the preparation of esters. which are useful as plasticizers for other organopolysiloxane rubbers and resins.

What I claim as new and desire to secure by Letter Patent of the United States is:

1. The process for forming intercondensed organopolysiloxanes containing carboxyalkyl siloxyunits and siloxy units free of silicon-bonded carboxyalkyl groups but containing silicon-bonded organic radicals selected from the class consisting of, monovalent hydrocarbon radicals and substituted monovalent hydrocarbon radicals, which process comprises heating an aqueous solo?" tion, of a. carboxyalkylp lysiloxane in which the .carboxy group is separated from the silicon atom by from -2 to 4 carbon atoms with and an organoalkoxysilane of the:

where R is a; member selected from the class, comisting" of monovalent hydrocarbon radicals. and halogenated 3. The process as in claim 1 in which the organo alkoxysilane is dimethyldiethoxysilane.

4. The process as in claim 1 in which the carboxyalkylpolysiloxane is composed of recurring structural units of the formula 6 and the orgauoalkoxysilane is dimethyldiethoxysilane.

References Cited in the file of this patent UNIT ED STATES PATENTS Sommer 'Oct. 25, 1955 Speier Nov. 15, 1955 

1. THE PROCESS FOR FORMING INTERCONDENSED ORGANOPOLYSILOXANES CONTAINING CARBOXYALKYL SILOXY UNITS AND SILOXY UNITS FREE OF SILICON-BONDED CARBOXYALKYL GROUPS BUT CONTAINING SILICON-BONDED ORGANIC RADICALS SELECTED FROM THE CLASS CONSISTING OF MONOVALENT HYDROCARBON RADICALS AND SUBSTITUADED MONOVALENT HYDROCARBON RADICALS, WHICH PROCESS COMPRISES HEATING AN AQUEOUS SOLUTION OF A CARBOXYALKYLPOLYSILOXANE IN WHICH THE CARBOXY GROUP IS SEPARATED FROM THE SILICON ATOMS BY FROM 2 TO 4 CARBON ATOMS WITH AND AN ORGANOALKOXYSILANE OF THE FORMULA 